Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$90.28	3.179%	$93.15	$93.15	$93.15	$93.20
Purchase #2	$174.65	5.797%	$184.7745	$184.77	$184.75	$184.80
Purchase #3	$140.45	5.203%	$147.7576	$147.76	$147.75	$147.80
Purchase #4	$29.58	5.703%	$31.2669	$31.27	$31.25	$31.30
Purchase #5	$78.40	4.458%	$81.8951	$81.90	$81.90	$81.90
Purchase #6	$149.93	3.861%	$155.7188	$155.72	$155.70	$155.70
Purchase #7	$67.89	6.233%	$72.1216	$72.12	$72.10	$72.10
7 purchase totals =	$731.18		$766.6845	$766.69	$766.60	$766.80